Overwintering Your Hibiscus
How should I overwinter my hibiscus?
Let’s start by identifying the type of hibiscus you are growing. A tropical hibiscus (Hibiscus rosa-sinensis) needs to move indoors for winter. Place it in front of a bright sunny window and treat it like a houseplant. You just might be rewarded with flowers throughout the winter. Or move the plant to a bright window in a cool room and water just often enough to keep the plant alive but not producing new growth. This is more stressful on the plant but is often the only option for gardeners with limited indoor growing space.
Allow your hardy hibiscus are (Hibiscus coccineus or Hibiscus moscheutos) are hardy in zones 4 to 9 and should be allowed to stand for the winter in colder zones. Research has shown leaving perennials stand for winter increases their hardiness. You can cover the base with evergreen boughs or straw after the ground freezes for a bit of additional winter insulation. In late winter cut the stems back to 6 or 12 inches above ground. These stem remnants mark the location of the late-to-emerge hibiscus. One summer mine did not start growing until early July. But it quickly made up for lost time and rewarded me with a full sized plant and beautiful blooms.
Rose-of-Sharon (Hibiscus syriacus) is a late blooming shrub rated hardy in zones 5 to 8 (though I have seen zone 4 and 9 gardeners push the limits). Proper care throughout the season will help insure its winter survival. Zone 5 and those daring zone 4 gardeners will lose these plants when winter temperatures are extreme or quite variable. Nothing you can do but hope for consistent cold and good snow cover. That is the best winter protection for all our plants.